Prestressed electric insulator assembly

ABSTRACT

An electric insulator assembly having a ceramic main body compressively prestressed to a high degree and preferably in excess of its design load by an imbedded tensioned, multilayer loop of high-strength filament. The adjustable prestressing means comprises wedge means extending transversely of one or both end caps and readily accessible for adjustment throughout the service life of the installed assembly. The passage enclosing the loop is located symmetrically of a suspension insulator and asymmetrically of a cantilever-type assembly, the interior being provided with cooperating insulative filler components sealed to the loop and to the passage walls.

United States Patent [72] Inventor Richard H. Dougherty 4504 Van Alden Ave.. Tomlin. Calil. 91356 [21] Appl. No. 854,884

[22] Filed Sept. 3, 1969 [45] Patented July 13,1971

{54] PRBS'I'RESSED ELECTRIC INSULATOR Primary Examiner- Laramie E. Askin Attorney-Sellers and Brace ABSTRACT: An electric insulator assembly having a ceramic main body compressively prestressed to a high degree and preferably in excess of its design load by an imbedded tensioned, multilayer loop of high-strength filamentv The adjustable prestressing means comprises wedge means extending transversely of one or both end caps and readily accessible for adjustment throughout the service life of the installed assembly. The passage enclosing the loop is located symmetrically of a suspension insulator and asymmetrically of a cantilever-type assembly, the interior being provided with cooperating insulative filler components sealed to the loop and to the passage walls.

PATENTED JUL 1 319?] SHEET 1 OF 2 W W a 0 W A E MM 4? H I w M m Z W m 4 m w wwww i V Hufiw H H b M g 0 i i M MQ a w PATENTEDJULIBIBH 3.592 959 SHEET 2 BF 2 /1 TTOEA/EVE) PRESTRESSED ELECTRIC INSULATOR ASSEMBLY This invention relates to electric insulator assemblies and more particularly to an improved, lighter weight, high load capacity insulator featuring novel means for carrying the mechanical design load by an imbedded prestressed loop to place the main body of the insulator in compression.

Much effort has been extended in attempts to increase the load-carrying capacity of insulators and yet reducing the weight and amount of material therein. It is well known that suitable ceramic materials having the requisite dielectric characteristics are relatively weak as respects their tensile and bending load strengths and relatively strong in sustaining coni pressive loads. With these characteristics in mind, designers have proposed numerous expedients for utilizing nonceramic materials interiorly of the ceramic material to carry a major portion of tensile and bending loads. However, prior proposals having these objectives are subject to numerous shortcomings and disadvantages sought to be obviated by the present invention.

The present invention contemplates an endless loop of fine. high-strength, nonconductive filaments assembled in layers and assembled on a form to assure that all individual convolutions will be uniformly stressed under design load conditions. High-strength glass fiber is particularly suitable and the convolutions of these fibers are bonded into a mass of uniform cross section while confined and supported under suitable ten sion.

The bonded fiber loop is housed lengthwise of a passage through th ceramic main body with its return bend portions exposed beyond the opposite ends of this body. End caps seated over the return bend portions and bearing against the opposite ends of the insulator enclose transversely extending wedge means operable as the wedges are loaded to place the loop in high tension while forcing the end caps against the insulator body to compress it under a load corresponding to the tensile load imposed on the loop by the wedges. The passage is filled with mating filler members held in assembled position against the loop and the passage walls by adhesive. The end cap cavity enclosing the return bend portions of the loop are likewise sealed with a suitable compound. The wedge adjusting means is readily accessible at all times through the side of the end cap in order that the prestressing can be adjusted at any time under live powerline conditions and without disturbing the installed condition of the insulator. The invention is equally suitable for use on both suspension, compression and cantilever type insulators, the prestressed loop being offset above the longitudinal center in the latter type for maximum effectiveness.

Accordingly. it is a primary object of the present invention to provide an improved lighter-weight higher-strength prestressed electric insulator assembly.

Another object of the invention is the provision of a simplified and highly prestressed insulator assembly utilizing an imbedded member prestressed in tension to a value adequate to carry normal loads and serving to maintain the insulator body prestressed in compression.

Another object of the invention is the provision of an improved, lightweight high dielectric insulator featuring wedge means adjustable transversely of the longitudinal axis of the insulator for prestressing the insulator assembly.

These and other more specific objects will appear upon reading the following specification and claims and upon considering in connection therewith the attached drawing to which they relate.

Referring now to the drawing in which a preferred embodi merit ofthe invention is illustrated:

FIG. 1 is a vertical sectional view through one preferred em bodiment of the invention incorporated in a vertical-type insulator:

FIG. 2 is a fragmentary cross-sectional view on an enlarged scale taken along line 2-2 on FIG. I;

FIG. 3 is a transverse sectional view taken along line 33 on F IG. 2;

FIG. 4 is a transverse sectional view taken along line 4-4 on FIG. 1;

FIG. 5 is a side elevational view with parts broken away showing the invention principles embodied in a cantilevertype insulator;

FIG. 6 is a top plan view on a reduced scale of the second embodiment; and

FIG. 7 is a cross-sectional view on an enlarged scale taken along line 7-7 on FIGv 5.

Referring initially and more particularly to FIGS. 1 to 4, there is shown one preferred embodiment of the invention prestressed insulator assembly designated generally 10, as designed for suspension use. As herein shown by way of example, the main body of the insulator comprises a plurality of identical components ll molded from suitable high-strength ceramic material in accordance with customary practice each having a longitudinal passage [2. The number of components 1 l assembled in axial abutment depends upon the voltage of the power line to be suspended from the lower end of the as sembly.

Passage 12 serves to house a high-strength, endless loop 15 constituting an important feature of the present invention. Loop 15 is preferably fabricated in the configuration illustrated in FIG. 1 from a single or a multiple strand tape of parallel filaments of high-strength nonconductive material. Glass fiber is particularly suitable but numerous other highstrength filament materials may be employed. Whether the filaments are assembled singly or in multiple they are wound in layers upon a mandrel or other form having the cross-sectional configuration of the interior dimensions of the illus trated flat loop. During the winding procedure the filaments are maintained under uniform light tension and the opposite sides are restrained by the aid of a suitable form to prevent spreading and inter weaving of the filaments. Epoxy or the like uncured resin-type adhesive is applied to the fiber or to the layers as these are formed and in such manner that the entire cross section is free of voids. The cross-sectional dimensions of the loop are such that the finished loop product has aneffective load-carrying capacity at least equal to and preferably substantially in excess of the normal operating load to be supported by the insulator assembly. After the resin has taken a set the finished loop is removed from the winding form and is ready for endwise assembly through passage 12 of the aligned insulator elements 11, 1!.

Before assembling loop 15 through the insulator elements, molded semicylindrical ceramic sections l7, 17 are assembled about the parallel midsections of loop 15 in the manner best il' lustrated in FIG. 4. It will be noted that sections 17 are contoured to fit about the interior surface and the opposite sides of loop 15 and to have a snug sliding fit with passage [2.

The components employed to prestress loop 15 and to hold the main body components assembled will be best understood from a consideration of FIGS. l, 2 and 3. The components'are identical at both ends of the insulator and, accordingly, a description of one set will suffice. These include a cup-shaped end cap 20 having a generally rectangularly shaped recess 21 opening through the bottom end thereof. The lip end 23 of the end cap is circular and includes an end wall 24 through which cavity 2| opens as is made clear by FIGS. 2 and 3.

The return bend portion 16 of loop 15 is supported in a U- shaped saddle member 26 formed on its exterior with a groove 27 snugly seating the interior and opposite sides of return hend [6. The transverse opening between the legs of saddle member 26 is in alignment with rectangular openings 28 formed in the opposite sidewalls of end cap 20.

Extending across the outer surface of end wall 24 is a rectangular bearing plate 29 having a flat bottom surface 30 and upwardly converging camming surfaces 3| on its opposite lace. Bearing against and sliding along camming surfaces 3], 31 are a pair of similar wedge members 32, 33. Their upper flat sides bear against the bight portion 34 of saddle member 26 whereas their upwardly converging lower surfaces 37 are inclined similarly to and bear directly against surfaces 31 of bearing plate 29. The means for adjusting wedge members 32,

33 toward one another comprises a capscrew 40 passing loosely through an opening in wedge 32 and mating with threads 4l in the aligned opening of wedge member 33.

The assembly and prestressing of the described insulator assembly will be readily apparent from the foregoing description of the end cap assembly. initially loop and the filler elements 1?, 17 are assembled lengthwise of passage 12 through the main body of the insulator. This process is carried out after first applying a suitable high dielectric adhesive 45 to all surfaces of the loop, passage 12 and elements H to seal the parts together and to exclude all voids, gas, moisture and foreign matter from the central passage. This assembly operation having been accomplished, the return bend portions [6 ofloop l5 will protrude from the opposite ends of the insulator. Adhesive is applied to groove 27 of saddle member 26 and installed within the return bend. End cap 20 is then telescoped over the loop until bottom end wall 24 seats against the adjacent end of the insulator. The next step is to insert bearing plate 29 through one end of the openings 28 with its flat surface 30 resting against end wall 24, it being noted that the opposite ends of this plate seat snugly within the recess formed by lip 23 and end wall 24 (FIG. 2). Wedge members 32, 33 are now inserted through openings 28 and pressed toward one another along the inclined surfaces 31, 31. Capscrew 40 is assembled to the wedge members following which similar assembly steps are performed at the opposite end of the insulator.

With both ends assembled as described cap screws 40 are gradually tightened forcing the wedges associated with each toward one another and gradually applying powerful tensioning forces to loop [5. After loop l5 has been tensioned to a desired load stress, usually in excess of the load capacity of the insulator assembly, potting or sealing compound 48 is charged into the opposite ends of the cavities 2|.

Referring now to FIGS. 5 through 7, a cantilever embodiment of the insulator assembly is shown wherein the same or similar parts are identified by the same reference characters as in FIGS. 1 to 4 but distinguished therefrom by a prime. In general, the two assemblies are very similar to one another, a principal difference being that the passage 12' housing loop I5 is offset parallel to and above the longitudinal axis of the main body 11' of the insulator. It will also be observed from FIG. 7 that this main body is generally elliptical in cross section with its major axis lying in a vertical plane.

One end cap 20' is provided with an arcuate base 50 contoured to fit snugly against a support structure, such as pole 5], to which it may be anchored by bolts 52. The other end cap at the outer end of the main body is provided with any suitable cable supponing and clamping structure 55 for a power cable 56.

In all other respects, the FIG. 5 to 7 embodiment is con slructed, assembled and prestressed in the same manner described above in connection with FIGS. 1 to 4. Since the tensioning loop 15' is located off center and above the main axis of the assembly, it will be apparent that the tension ap plied to this loop by tightening capscrews 40 is effective to compress the upper half of the insulator body to a greater extent than the lower half, as is appropriate and desirable in counteracting the greater tensile forces present in the upper half of a cantilever support.

it will be apparent from the foregoing that the described prestressed insulator assemblies utilize a minimum weight and amount of ceramic material since the major load and bending stresses imposed on the assembly are counteracted in total or major part by the prestressed high-strength loops [5, l5.

While the particular prestressed high-tension insulator as sembly herein shown and disclosed in detail is fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention.

I claim:

I. An electric insulator assembly comprising an elongated main body of ceramic material having a passage from end toend thereof, an endless loop of high strength nonconductive filaments bonded together with resinous material, said loop extending through and projecting from at least one end of said passage, separate one-piece cup-shaped end cap means each having a base end seated against a respective end of said main body and embracing the adjacent return bend portion of said loop, means extending transversely of each of said end cap means and interposed between the base end thereof and the return bend portion of said loop for anchoring the opposite ends of said loop to a respective one of said end cap means, one of said last-mentioned means including adjustable means effective as it is adjusted transversely of said end cap means to preload said loop in tension and said insulator main body in compression, and means including nonfluid insulating material filling the voids of said passage and ofsaid end caps and hermetically sealing the same closed to provide a sealed insulator assembly free ofliquid and voids.

2. An insulator assembly as defined in claim 1 characterized in that said nonfluid insulating material includes high dielectric preformed filler means contoured to fit loosely during assembly about the parallel opposite sides of the stretched loop and substantially filling the portions of said passage through the insulator body not occupied by said loop including bonding means bonding the same to the juxtaposed surfaces of said loop and of said passage.

3. An insulator assembly as defined in claim 1 characterized in that said adjustable means includes elongated wedgeshaped means extending crosswise of said one end cap and effective as said adjustable means is tightened to increase the pressure between the base end of each end cap and the juxtaposed end of said insulator main body.

4. An insulator assembly as defined in claim 3 characterized in that said wedge-shaped means includes a pair of aligned wedge members having their smaller ends projecting toward one another crosswise of said one end cap, and said adjustable means including bolt means extending through aligned passages lengthwise of said wedge members for forcing the same toward one another to prestress said loop and said main body to a desired load stress.

5. An insulator as defined in claim 1 characterized in the provision of aligned large area openings in the sidewall of said one cup-shaped end cap, bearing plate means sized for insertion through said aligned openings and adapted to bear against the interior side of the base end of said end cap, said adjustable means including a pair of aligned wedge members facing in opposite directions located between the return bend portion of said loop and the adjacent face of said bearing plate, and screw means extending lengthwise between said wedge members effective as the same is tightened to shift said wedge members transversely of the longitudinal axis of said insulator assembly and thereby prestress said loop and said main body.

6. An insulator assembly as defined in claim 5 characterized in the provision of a saddle member shaped to seat within the return bend portion of said loop and shaped on the other side thereofto seat against one face of said pair of wedge members.

7. An insulator assembly as defined in claim 5 characterized in that one of said wedge members has a threaded bore, and said screw means comprising a cap screw extending loosely through a bore lengthwise of the other wedge member into mating engagement with said threaded bore.

8. An insulator assembly as defined in claim 5 characterized in that said bearing plate has the surfaces thereof in contact with said wedge members sloping at an angle corresponding to the slope of the wedge member in contact therewith.

9. An insulator assembly as defined in claim 5 characterized in that said bearing plate and adjacent surface of the base end of said cap member are shaped to retain said bearing plate against endwise movement when seated on said base end.

It). An insulator assembly as defined in claim I characterized in that the axis of said passage lengthwise of the main body of the insulator is coincident with the longitudinal axis of the main body.

I]. An insulator assembly as defined in claim 1 characterized in that the axis of said passage lengthwise of the main body of the insulator is parallel to but offset laterally to one side of the insulator axis 12. An insulator assembly as defined in claim 11 characterized in that a bisector plane passing through both sides of said loop lies normal to a diametric plane through the longitudinal axis of said main body.

13. An insulator assembly as defined in claim 1 characterized in that each of said end caps includes similar adjustable means extending transversely through each one thereof.

14. An insulator assembly as defined in claim 1 characterized in that the interiors of said end caps contain a charge 

1. An electric insulator assembly comprising an elongated main body of ceramic material having a passage from end-to-end thereof, an endless loop of high-strength nonconductive filaments bonded together with resinous material, said loop extending through and projecting from at least one end of said passage, separate one-piece cup-shaped end cap means each having a base end seated against a respective end of said main body and embracing the adjacent return bend portion of said loop, means extending transversely of each of said end cap means and interposed between the base end thereof and the return bend portion of said loop for anchoring the opposite ends of said loop to a respective one of said end cap means, one of said lastmentioned means including adjustable means effective as it is adjusted transversely of said end cap means to preload said loop in tension and said insulator main body in compression, and means including nonfluid insulating material filling the voids of said passage and of said end caps and hermetically sealing the same closed to provide a sealed insulator assembly free of liquid and voids.
 2. An insulator assembly as defined in claim 1 characterized in that said nonfluid insulating material includes high dielectric preformed filler means contoured to fit loosely during assembly about the parallel opposite sides of the stretched loop and substantially filling the portions of said passage through the insulator body not occupied by said loop including bonding means bonding the same to the juxtaposed surfaces of said loop and of said passage.
 3. An insulator assembly as defined in claim 1 characterized in that said adjustable means includes elongated wedge-shaped means extending crosswise of said one end cap and effective as said adjustable means is tightened to increase the pressure between the base end of each end cap and the juxtaposed end of said insulator main body.
 4. An insulator assembly as defined in claim 3 characterized in that said wedge-shaped means includes a pair of aligned wedge members having their smaller ends projecting toward one another crosswise of said one end cap, and said adjustable means including bolt means extending through aligned passages lengthwise of said wedge members for forcing the same toward one another to prestress said loop and said main body to a desired load stress.
 5. An insulator as defined in claim 1 characterized in the provision of aligned large area openings in the sidewall of said one cup-shaped end cap, bearing plate means sized for insertion through said aligned openings and adapted to bear against the interior side of the base end of said end cap, said adjustable means including a pair of aligned wedge members facing in opposite directions located between the return bend portion of said loop and the adjacent face of said bearing plate, and screw means extending lengthwise between said wedge members effective as the same is tightened to shift said wedge members transversely of the longitudinal axis of said insulator assembly and thereby prestress said loop and said main body.
 6. An insulator assembly as defined in claim 5 characterized in the provision of a saddle member shaped to seat within the return bend portion of said loop and shaped on the other side thereof to seat against one face of said pair of wedge members.
 7. An insulator assembly as defined in claim 5 characterized in that one of said wedge members has a threaded bore, and said screw means comprising a cap screw extending loosely through a bore lengthwise of the other wedge member into mating engagement with said threaded bore.
 8. An insulator assembly as defined in claim 5 characterized in that said bearing plate has the surfaces thereof in contact with said wedge members sloping at an angle corresponding to the slope of the wedge member in contact therewith.
 9. An insulator assembly as defined in claim 5 characterized in that said bearing plate and adjacent surface of the base end of said cap member are shaped to retain said bearing plate against endwise movement when seated on said base end.
 10. An insulator assembly as defined in claim 1 characterized in that the axis of said passage lengthwise of the main body of the insulator is coincident with the longitudinal axis of the main body.
 11. An insulator assembly as defined in claim 1 characterized in that the axis of said passage lengthwise of the main body of the insulator is parallel to but offset laterally to one side of the insulator axis.
 12. An insulator assembly as defined in claim 11 characterized in that a bisector plane passing through both sides of said loop lies normal to a diametric plane through the longitudinal axis of said main body.
 13. An insulator assembly as defined in claim 1 characterized in that each of said end caps includes similar adjustable means extending transversely through each one thereof.
 14. An insulator assembly as defined in claim 1 characterized in that the interiors of said end caps contain a charge of sealing compound effective to exclude moisture and foreign matter.
 15. An insulator assembly as defined in claim 1 characterized in that passage through said main body includes at least one pair of ceramic filler members shaped to fit about the sides of said loop and to have a close sliding fit within said passage, and sealing material filling the remainder of said passage to preclude the entry of moisture and the like adversely affecting the dielectric properties of said insulator assembly. 